Channel quality information is important base for the network side to perform a variety of adaptive adjusting and scheduling. Channel quality is quantized in Long Term Evolution (LTE) into 4-bit Channel Quality Indicator (CQI) each with an index corresponding to combination of a modulation scheme and a coding rate. To calculate CQI, a UE has to assume transmission scheme of Physical Downlink Shared Channel (PDSCH) in view of its transmission mode. For example, transmission schemes of PDSCH are assumed as illustrated in FIG. 1 for calculation of CQI defined in LTE Release (Rel-9).
In each of the Transmission Modes (TMs) 4 to 6, a User Equipment (UE) has to calculate from detection of Cell-specific Reference Signal (CRS) and report its recommended Precoding Matrix Indicator (PMI), and the UE reports CQI assuming an evolved Node B (eNB) uses its reported PMI. In the TM7, a non-codebook precoding scheme is adopted, and the UE only reports CQI to the eNB, and the eNB calculates a precoding or shaping vector. In the TM8, both PMI and non-PMI feedback schemes can be supported, and the UE can generates report parameter (PMI/Rank Indication (RI)/CQI or CQI) from detection of CRS in a high-layer configured feedback scheme and specific report mode.
In a Long Term Evolution-Advanced (LTE-A) system, newly defined Channel State Information-Reference Signal (CSI-RS) is introduced so as to support higher-order Multiple-Input Multiple-Output (MIMO) transmission (support up to 8 data layers) as well as a multi-cell joint processing function in a subsequent release. In the TM9, a Demodulation Reference Signal (DMRS) based demodulation scheme is adopted, and CSI-RS only functions for detection instead of demodulation. Like the TM8, the eNB can configure in high-layer signaling a report mode of the UE as the PMI or non-PMI form. In the TM9, the UE configured without PMI reporting reports CQI based upon CRS, while the UE configured with PMI reporting has to generate CQI/PMI/RI or other report information from detection of CSI-RS. In this case, with the absence of a CSI-RS based feedback scheme, the UE calculating CQI can not assume which CSI-RS based transmission scheme is adopted for PDSCH and consequently can not report channel state based upon CSI-RS when calculating CQI.